355 © Springer Nature Singapore Pte Ltd. 2019 A. Varma, D. K. Choudhary (eds.), Mycorrhizosphere and Pedogenesis, https://doi.org/10.1007/978-981-13-6480-8_20 Soil Metagenomics: Unculturable Microbial Diversity and Its Function Deep Chandra Suyal, Divya Joshi, Prasen Debbarma, Ravindra Soni, Biplab Das, and Reeta Goel 1 Introduction Soil is a dynamic and most vibrant ecosystem in nature. It defnitely serves as a vast reservoir for both known and unknown microorganisms inhabiting in different niche within the particular soil ecosystem. Each soil fraction i.e. sand, silt, clay and organic matter offer limitless diverse microhabitats for different soil inhabiting microbes (Rui et al. 2017). The reason behind such rich habitat is due to the soil environment which is so variable ranging from μm to mm scale and harbor distinct microbial communities. However, the surroundings of distinct niche may vary with microbial diversity, their abundances, biotic and abiotic features. Therefore, distinct microhabitat is dwelled by those microorganisms which showed the ability to adapt the environment and established the colony to the particular niche. The most important factors that infuence the microbial composition in the soil ecosystem may include the properties of soil physico-chemical features, soil pH, moisture and temperature (Fierer et al. 2009; Eccles et al. 2018). However, micro- organisms are inhabited in only about 1% of the total available soil surface area regardless of its great biomass present in the soil ecosystem. Furthermore, it is esti- mated that microbes which are dormant at a particular given time accounts for as far as >95% of the overall biomass pool of microorganisms (Blagodatskaya and Kuzyakov 2013). Therefore, comprehending the structure of indigenous microbial diversity and dynamicity at present scenario stands one of the most challenging tasks in current soil ecology. D. C. Suyal (*) · D. Joshi · P. Debbarma · R. Goel Department of Microbiology, CBSH, G.B. Pant University of Agriculture and Technology, Pantnagar, Uttarakhand, India R. Soni · B. Das Department of Agricultural Microbiology, College of Agriculture, Indira Gandhi Krishi Vishwavidyalaya, Raipur, Chhatisgarh, India 20